[Bicycle Bob]

Sizing is like a wetting agent, and something to protect the fiber during processing. Glass fibers typically lose a lot of strength from mutual rubbing even with it. The sizing can vary according to the intended resin to speed up the impregnation and maximize adhesion. Metal coatings are quite rare, used to add qualities such as electrical conduction for lightning protection. The Cook-Gordon mechanism is quite automatic, provided the resin is under 20% the tensile strength of the fiber. If you use really good glue with weak fiber, it will be able to crack right through.